Obesity and Some Behavioral Biology

All right, weight regulation is really damn complex.  I am going to admit that upfront.  It involves many of the things we’ve talked about on this website in reference to brains—the body, multiple brain systems, complex interactions, and so forth.  Sure, most of the research does not include much context or culture or even environmental interaction, but then again, the research is aimed at getting at some basic biology, at understanding the mechanisms and processes involved in weight regulation.

So, what do we have?  In no particular order other than my impressions from reviewing the literature, (1) the importance of body-based systems in appetite and weight regulation, (2) the usefulness of allostasis in understanding weight, energy, eating and activity regulation; (3) satiation and appetite as more important in obesity than energy balance, which generally plays a modifying role; (4) the need to consider weight gain and weight loss separately; (5) the role of physical activity might play in driving weight regulation; and (6) the considerable limitations of “will power” to affect any of the above points, due to how our brains and bodies are set up and the considerable mismatch between our western ideology of self and how we actually work.

In this post I’ll cover stuff on the first four.  See Greg’s comment on Genetics and Obesity for more on #5-Activity, and for now, I hope that the ability of cognitive control over hormone release and lower brain systems should at least be fairly obvious.  (As for getting all this done by yesterday, I had a senior colleague spring a surprise guest lecture on me—so that meant dropping lots of on-going stuff to get that ready… Excuses, excuses.) 

So, body-based systems.  Two hormones, leptin and ghrelin, play a powerful role in shaping energy regulation, eating and weight.  The trick is that leptin is released by white adipose tissue (fat) and gherlin by the stomach and intestine.  Both have direct effects in our brains, overturning our general view of the brain as a master organ.  Leptin and gherlin act in concerted fashion, like many regulatory systems in the body (e.g., sympathetic and parasympathetic peripheral nervous systems).  For example, Zigman and Elmquist (2003) (pdf) liken them to the Yin and Yang of body weight control.  They characterize leptin as “a molecular signal of energy abundance” and gherlin as “an important indicator of energy insufficiency.”  In mice, increasing circulating leptin can decrease food intake, while gherlin stimulates feeding.  However, neither has proven broadly effective as dietary drugs, because weight and energy regulation are not driven by one sole hormone except in rare genetic deficiency cases.

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Genetics and Obesity

In my medical anthropology class, we’ve been reading Gina Kolata’s Rethinking Thin: The New Science of Weight Loss and the Myths and Realities of Dieting.  Kolata argues for a biological approach to obesity, that weight is largely under genetic control and that there is no ideal diet which is going to help all people lose weight.  In other words, Kolata is taking up the “nature” side of the nature/nurture debate, with a direct critique of the idea that if overweight people could simply use their willpower and follow the age-old recommendation of eat less and exercise more, they would be ideally thin like the beautiful people we see on television—the Brad Pitts and Angelina Jolies of the world. 

Kolata sums up these points in a very amusing interview on The Colbert Report.  As Fat Fu summarizes about Kolata, “you can actually learn something about the state of the science. And which don’t conclude with exhortations to diet or insinuations that fat people are lazy and ignorant. In fact she doesn’t think diets work.” 

I like Kolata’s book, which is why I assigned it in my class.  And I certainly see the weight of the evidence as supporting many of her main points: heritability and biological regulation of body weight, as well as the absurdity of an “ideal diet” that will simply work for everyone (that’s called ideology, folks).  But Kolata gives us an approach that recreates the mind/body and culture/biology dichotomies, and resorts to a genetic determinism that both obscures the genetics and doesn’t leave much room for anthropology.  For example, she uses one study, a classic one by Stunkard et al. in 1990, to tell us that “70 percent of the variation in people’s weight’s may be accounted for by inheritance,” which is greater heritability than with “mental illness, breast cancer or heart disease.” 

I’ll admit, I am not the biggest fan of twin studies.  They are generally done in western populations without much variance in environment or development and with relatively homogenous populations.  In public, these researchers generally claim the higher range of heritability estimates.  And perhaps most bothersome, these studies seem to provide us with a “why” that is not really there—“genetic” becomes tantamount to cause. 

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The history of mind-altering mechanisms

Katherine MacKinnon of St. Louis University just dropped me a line to point out a recent book review in The New York Times, I Feel Good, by Alexander Star. Star reviews the book, On Deep History and the Brain, by Daniel Lord Smail (University of California Press). Amazon raters are giving it 4.5 stars at the moment, if you want to check it out through the bookseller. Normally, I’d trust Daniel to write our best stuff about ‘mind-altering’ chemicals of all sorts, but this book review just set me to thinking, so I thought I’d put my own two cents in.

Smail wants to tell the story of humanity as a series of ‘self-modifications of our mental states,’ according to the reviewer Star:

We want to alter our own moods and feelings, and the rise of man from hunter-gatherer and farmer to office worker and video-game adept is the story of the ever proliferating devices — from coffee and tobacco to religious rites and romance novels — we’ve acquired to do so. Humans, Smail writes, have invented “a dizzying array of practices that stimulate the production and circulation of our own chemical messengers,” and those devices have become more plentiful with time. We make our own history, albeit with neurotransmitters not of our choosing.

Smail is really a historian, but his venture into a kind of neuro-history shows the robustness of the emerging awareness that the brain is shaped by what humans do. Star points out that most ‘macro-history’ these days — long, sweeping accounts of human evolution and what is sometimes called something prosaic like the ‘rise and fall of civilizations’ — is not being written by historians, but rather by folks like Jared Diamond. In contrast, Smail is a medieval historian.

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Glucose, Self Control and Evolution

Galliott et al. published a 2007 article entitled “Self Control Relies on Glucose as an Energy Source: Willpower Is More Than Self Control” (pdf here). Recently Vaughan at Mind Hacks and Dave at Cognitive Daily have taken up the topic with some creative posts.  Vaughan writes that Resisting Temptation Is Energy Intensive, focusing on the role of attention and the prefrontal cortices.  Dave posts on Practicing Self-Control Takes Real Energy, and includes a recreation of the research procedure (with video) and an informative summary.  I also mentioned some of this research in a previous post on Willpower as Mental Muscle.

What I want to add today is that this sort of research has implications for our understanding of brain evolution and for social problems like obesity and addiction.  Focusing attention and using one part of your brain against another part, that takes significant energy.  The brain is already our most energy-intensive organ, so adding the demands of “self control” on top of that is likely to have presented some adaptive issues in the past.  Put differently, it’s unlikely to expect that we’ve evolved to be able to maintain self control over extremely long periods of time (say, months), simply because such problems rarely presented themselves in the past (there were few adaptive benefits) and because the energetic costs of doing so would have been quite high.

Diets are often marked by periods of effortful weight loss, followed by a slide back, where weight is regained.  That pattern is not simply a matter of mind over matter, of willpower so we can match a cultural and cognitive ideal.  It’s hard for people to maintain sustained mental efforts, it costs energy, and there’s little evolutionary reason to expect everybody’s brains to suddenly begin cooperating with what our culture tells us we should be able to do.

The Family Dinner Deconstructed

National Public Radio had a radio broadcast yesterday morning on “The Family Dinner Deconstructed.”  Here’s the blurb: “The ritual of a family dinner has been praised as an antidote to bad grades and bad habits in kids. But as researchers look closer at the family dinner, they raise the question: Is it the mere act of eating together that counts, or is it that strong families are already more likely to have a family dinner?” 

The reporter does a wonderful job talking with a variety of researcher to focus in on the proximate features of the family dinner—conversations, relationships, rituals, emotions—and how they can impact physical and mental health.  For example, the quality of conversations at mealtime was a better predictor of reading development than parents actually reading to their children.  But what mattered was the content on dinner conservation, that it was complex and “rich with explanation, story telling, and more.”  Similarly, for physical and mental development (for example, eating disorders), specific behaviors at dinner proved important: roles assigned (setting the table, beginning and end to dinner); a genuine concern about daily activities; and a sense of empathy and concern for each other. 

While the radio cast pushes a double-blind study to “determine” the specific effects of a good-quality family dinner versus dinner-as-usual, the announcer rightly acknowledges that doing such research is a daunting prospect.  I would add that an ethnographic approach that builds on this educational and psychological research and that teases out the relationships between dinner, family interaction, and development as a joint physical-mental phenomenon could also add some great insights.

Sleep, Eat, Sex – Orexin Has Something to Say

Blogging on Peer-Reviewed ResearchOrexin is a neuropeptide which is released by the posterior lateral hypothalamus, and is linked to wakefulness and sleep, appetite regulation, and the motivation of sexual and addictive behaviors.  One apt way to think about it is as a hormone in the brain, combining some of the popularly conceived effects of adrenaline and testosterone into one. 

(Don’t get too excited now!  I am just trying to give you a way to think about it, that orexin works to promote arousal and response…)

I am writing a post on the links of orexin to appetitive behavior, particularly addiction, but I’ve generated a lot of material.  So I am going to give you this one first, which summarizes aspects of orexin (also known as hypocretin) and neurological function with respect to sleep, appetite and sex. 
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